The thirty-four drawings, all studies of animals, came from a 17th-century album that once contained 160 drawings of birds by the father and son artists Pieter Holsteijn the Elder and the Younger. The album was donated to the Noord-Hollands Archief in 1888, but the drawings by Frans Post had probably been part of it for centuries. The Brazilian animal studies were completely overlooked until De Bruin found them in 2010.